Depressive disorders are among the most common conditions a clinician will see, and among the most lethal when missed. The DSM-5-TR groups them into a single chapter — major depressive disorder, persistent depressive disorder, premenstrual dysphoric disorder, disruptive mood dysregulation disorder, and the substance/medication-induced and other-medical-condition variants — separated from the bipolar spectrum by the absence of any lifetime manic or hypomanic episode. Major depressive disorder (MDD) is defined by at least two weeks of pervasive low mood or Anhedonia, with five or more characteristic symptoms producing functional impairment. Diagnosis is clinical; laboratory testing exists to rule out medical mimics, not to confirm depression. First-line treatment for moderate-to-severe MDD combines an SSRIs or SNRIs antidepressant with evidence-based psychotherapy, with neuromodulation reserved for treatment resistance or urgent severity. The clinical bottom line: ask about suicide every visit, watch for missed bipolarity, and treat to remission rather than response.

Depression is the leading psychiatric contributor to global disability and a major driver of suicide. Population data are remarkably consistent across high-income countries, though prevalence varies with measurement method and economic stress.

Prevalence and incidence

• Lifetime prevalence of MDD in U.S. adults is approximately 21%, with 12-month prevalence near 8-10%.^1-2
• Persistent depressive disorder (PDD) has a lifetime prevalence of roughly 3-6%.¹
• Premenstrual dysphoric disorder affects 1.8-5.8% of menstruating individuals.³
• Disruptive mood dysregulation disorder (DMDD) has a 6-12 month prevalence of 2-5% in children.¹

Demographics

• Female-to-male ratio is approximately 2:1 from adolescence through midlife, narrowing in older adulthood.^1-2
• Mean age of onset for MDD is the mid-20s, but first episodes occur across the lifespan.²
• Lifetime risk of suicide death in MDD is estimated at 4-6% in clinical samples, lower in community samples.⁴

Comorbidity

• Lifetime comorbidity with any anxiety disorder approaches 60%.²
• Substance use disorders co-occur in roughly one-quarter of patients with MDD.²
• Cardiovascular disease, diabetes, chronic pain, and stroke double the risk of incident depression and worsen its course.⁵

Risk factors

• Family history of mood disorder, with heritability estimates of 30-40% for MDD.⁶
• Childhood adversity, particularly sexual abuse and emotional neglect.⁵
• Female sex, postpartum period, perimenopause, and chronic medical illness.⁵
• Stressful life events, especially humiliating or entrapping losses.⁵

Depression is a heterogeneous syndrome, and no single neurobiological lesion explains it. Current models integrate monoamine signaling, stress-axis dysregulation, neuroplasticity, and circuit-level dysfunction within an inflammatory and genetic context.

Neurotransmitter systems

• The monoamine hypothesis posits deficient serotonergic, noradrenergic, and dopaminergic signaling, supported by the clinical efficacy of monoamine-targeting drugs and tryptophan depletion paradigms — though depletion alone does not induce depression in healthy controls.⁷
• Glutamatergic dysfunction, particularly NMDA receptor signaling, underlies the rapid antidepressant effect of ketamine and esketamine.⁸
• GABAergic deficits in cortical interneurons contribute to the rationale for neurosteroid antidepressants such as brexanolone and zuranolone.⁹

Neuroendocrine and inflammatory pathways

• Hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis with elevated cortisol and dexamethasone non-suppression is observed in a subset of patients, particularly those with melancholic features.¹⁰
• Elevated peripheral inflammatory markers (CRP, IL-6, TNF-alpha) are associated with depression and may identify patients more responsive to anti-inflammatory adjuncts.¹⁰

Circuits and imaging

• Hyperactivity of the subgenual anterior cingulate cortex (Brodmann area 25) and reduced dorsolateral prefrontal cortex activation are replicable findings in depressed patients.¹¹
• Hippocampal volume loss correlates with episode duration and is partially reversible with treatment.¹¹
• Aberrant connectivity within the Default mode network is associated with rumination.¹¹

Genetics

• Twin heritability for MDD is approximately 30-40%, lower than bipolar disorder or schizophrenia.⁶
• Genome-wide association studies have identified more than 100 significant loci, each of small effect.⁶
• The serotonin transporter promoter polymorphism (5-HTTLPR) gene-by-environment interaction has not replicated robustly in large meta-analyses.⁶

Environmental and psychosocial contributors

• Early-life adversity produces durable HPA-axis sensitization and methylation changes at glucocorticoid receptor genes.⁵
• Loss events, social defeat, and chronic interpersonal stress are the most consistent proximal triggers.⁵
• Sleep disruption, particularly reduced REM latency and increased REM density, is both a risk factor and a state marker.¹²

Diagnosis remains clinical and depends on a careful longitudinal history. The DSM-5-TR retains the depressive disorders as a chapter distinct from bipolar and related disorders, reflecting the field's recognition that lifetime mania changes the entire treatment frame.¹

Major depressive disorder (DSM-5-TR)

• At least five of nine symptoms during a two-week period, representing a change from baseline, with at least one being depressed mood or loss of interest/pleasure.¹
• The nine symptoms span depressed mood, anhedonia, weight or appetite change, sleep disturbance, psychomotor agitation or retardation, fatigue, worthlessness or excessive guilt, diminished concentration, and recurrent thoughts of death or suicide.¹
• Symptoms must cause clinically significant distress or functional impairment and not be attributable to a substance or another medical condition.¹
• There must be no history of a manic or hypomanic episode.¹
• The bereavement exclusion was removed in DSM-5; clinicians distinguish grief from a major depressive episode by symptom pattern and functional impact rather than by timing.¹

MDD specifiers

• With anxious distress, with mixed features, with melancholic features, with atypical features, with mood-congruent or mood-incongruent psychotic features, with catatonia, with peripartum onset, with seasonal pattern.¹
• Severity (mild, moderate, severe), course (single episode vs recurrent), and remission status (partial vs full) are also specified.¹

Persistent depressive disorder

• Depressed mood for most of the day, more days than not, for at least two years in adults (one year in children/adolescents).¹
• At least two of: poor appetite or overeating, insomnia or hypersomnia, low energy, low self-esteem, poor concentration, hopelessness.¹
• Subsumes the former DSM-IV dysthymic disorder and chronic MDD; specifiers indicate whether full MDE criteria have been met.¹

Premenstrual dysphoric disorder

• At least five symptoms in the final week before menses, improving within days of menses onset and minimal in the week post-menses, confirmed by prospective daily ratings over two cycles.¹
• Affective lability, irritability, depressed mood, or anxiety must include at least one core symptom.¹

Disruptive mood dysregulation disorder

• Severe recurrent temper outbursts grossly out of proportion to provocation, occurring on average three or more times per week, with persistent irritability between outbursts.¹
• Onset before age 10, diagnosis between ages 6 and 18, present in at least two settings.¹
• Created to address overdiagnosis of pediatric bipolar disorder; cannot coexist with oppositional defiant disorder, intermittent explosive disorder, or bipolar disorder.¹

Other depressive presentations

• Substance/medication-induced depressive disorder when symptoms develop during or shortly after intoxication, withdrawal, or medication exposure.¹
• Depressive disorder due to another medical condition (e.g., hypothyroidism, stroke, pancreatic cancer).¹
• Other specified and unspecified depressive disorders for clinically significant presentations that fall short of full criteria.¹

The textbook depressed patient is rare. Symptom expression varies by age, culture, sex, and comorbidity, and somatic complaints often dominate the presentation in primary care.

Core symptom clusters

• Affective: depressed mood, anhedonia, anxiety, irritability, emotional numbing.^1,14
• Cognitive: rumination, guilt, hopelessness, worthlessness, concentration deficits, indecisiveness, suicidal ideation.^1,14
• Somatic and neurovegetative: insomnia (typically early-morning awakening) or hypersomnia, appetite and weight change, fatigue, Psychomotor retardation or agitation, diurnal mood variation worse in the morning.^1,14

Subtypes and their tells

• Melancholic: profound anhedonia, mood non-reactivity, distinct quality of mood, early-morning awakening, marked psychomotor change, anorexia, excessive guilt.¹
• Atypical: mood reactivity preserved, leaden paralysis, hypersomnia, hyperphagia with weight gain, longstanding interpersonal rejection sensitivity.¹
• Psychotic: mood-congruent or mood-incongruent delusions or hallucinations; carries higher suicide risk and requires combined antidepressant-antipsychotic therapy or ECT.¹⁵
• Catatonic: stupor, mutism, posturing, waxy flexibility, echolalia or echopraxia; responsive to benzodiazepines and ECT.¹⁶
• Seasonal pattern: temporal relationship of episodes to a particular season, most often fall-winter onset with spring remission.¹
• Peripartum onset: onset during pregnancy or within four weeks postpartum per DSM-5-TR; clinicians often extend to 12 months postpartum.^1,17
• Mixed features: at least three manic/hypomanic symptoms during a depressive episode; flags increased risk of bipolarity and altered treatment response.¹

Course features

• Untreated episodes typically last 6-12 months; treated episodes shorten to 3-6 months.¹⁴
• Recurrence is the rule: 50% after one episode, 70% after two, 90% after three.¹⁴
• Each subsequent episode increases vulnerability to the next (kindling).¹⁴

Red flags requiring immediate escalation

• Active suicidal ideation with plan or intent, recent attempt, or access to lethal means.¹⁸
• Psychotic features, particularly command auditory hallucinations.¹⁵
• Catatonia or severe self-neglect with inability to maintain hydration or nutrition.¹⁶
• Postpartum depression with infanticidal ideation or psychotic features.¹⁷

Two errors dominate clinical practice: missing bipolar disorder in a patient who looks unipolar, and missing a medical or substance-induced cause in a patient who looks primary. Both are avoidable with a thorough history and a parsimonious workup.

Psychiatric differentials

• Bipolar I and II disorder: lifetime mania or hypomania reframes the diagnosis and contraindicates antidepressant monotherapy; screen with the MDQ or careful longitudinal history.¹⁹
• Persistent depressive disorder versus recurrent MDD: chronicity and the two-year duration distinguish PDD.¹
• Adjustment disorder with depressed mood: identifiable stressor, fewer symptoms, shorter course (<6 months after stressor resolves).¹
• Generalized anxiety disorder: shares insomnia, fatigue, concentration problems, but worry rather than anhedonia is core.¹
• Post-traumatic stress disorder: re-experiencing, avoidance, hyperarousal beyond depressive symptoms.¹
• Schizoaffective disorder: psychotic symptoms persist for two or more weeks in the absence of a major mood episode.¹
• Borderline personality disorder: chronic emptiness and reactive dysphoria can mimic depression but with characteristic interpersonal pattern and identity disturbance.¹
• Prolonged grief disorder: distinguished from MDD by yearning and preoccupation with the deceased rather than pervasive anhedonia and worthlessness.¹

Medical mimics (do not miss):

• Hypothyroidism, hyperthyroidism, Cushing syndrome, Addison disease.²⁰
• Vitamin B12, folate, and vitamin D deficiency.²⁰
• Anemia, obstructive sleep apnea, chronic infection (HIV, hepatitis C, neurosyphilis).²⁰
• Neurologic: stroke (especially left frontal), Parkinson disease, Huntington disease, multiple sclerosis, traumatic brain injury, dementia.²⁰
• Oncologic: pancreatic adenocarcinoma classically presents with depressive symptoms preceding diagnosis.²⁰
• Autoimmune: systemic lupus erythematosus, anti-NMDA receptor encephalitis.²⁰

Substance and medication-induced depression

• Alcohol, sedative-hypnotic, opioid, stimulant withdrawal.¹
• Interferon-alpha, corticosteroids, propranolol (modest signal), isotretinoin (mixed evidence), efavirenz, varenicline (FDA black-box removed in 2016).²⁰
• Hormonal contraceptives in vulnerable individuals.²⁰

A focused diagnostic interview takes 30-45 minutes and should map symptoms onto DSM criteria, screen for bipolarity, quantify suicide risk, and identify treatable medical contributors. Rating scales improve detection and measurement-based care, but they do not replace clinical judgment.

History elements that must not be skipped:

• Onset, duration, and course of current symptoms; prior episodes; treatment response; family history of mood disorder, suicide, and bipolarity.¹⁴
• Lifetime screen for mania or hypomania, including substance- or antidepressant-induced episodes.¹⁹
• Suicidal ideation, intent, plan, prior attempts, lethal means access.¹⁸
• Substance use, including alcohol, cannabis, opioids, stimulants, and benzodiazepines.¹⁴
• Trauma history, current psychosocial stressors, and protective factors.¹⁴
• Sleep, appetite, sexual function, and functional impairment in work, relationships, and self-care.¹⁴

Validated rating scales

• PHQ-9: 9-item self-report mapped to DSM criteria; cutoff ≥10 for moderate depression with sensitivity ~88% and specificity ~88%.²¹
• Hamilton Depression Rating Scale (HAM-D): 17-item clinician-rated; standard outcome measure in trials.²²
• Montgomery-Åsberg Depression Rating Scale (MADRS): 10-item clinician-rated, more sensitive to change than HAM-D.²³
• Beck Depression Inventory (BDI-II): 21-item self-report widely used in research and primary care.²⁴
• Edinburgh Postnatal Depression Scale (EPDS): perinatal-specific 10-item scale; cutoff ≥13.²⁵
• Columbia Suicide Severity Rating Scale (C-SSRS): structured suicide risk assessment.¹⁸

Physical exam and laboratory workup

• Vital signs, weight, neurologic screen, and inspection for signs of self-harm or systemic illness.²⁰
• TSH, CBC, comprehensive metabolic panel, vitamin B12, vitamin D in routine workup.²⁰
• HIV, RPR, urine toxicology when history suggests.²⁰
• Pregnancy test in reproductive-age patients before starting medication.²⁰
• EKG when prescribing QT-prolonging agents (citalopram >40 mg, TCAs) or in older adults.²⁶

Tests not to order routinely

• Brain MRI in the absence of focal neurologic findings, atypical course, or first episode after age 50.²⁰
• Dexamethasone suppression test, thyroid antibodies, or genetic testing as part of routine MDD workup.²⁰
• Pharmacogenomic testing is not currently endorsed by APA or NICE as a routine guide to antidepressant selection, though evidence is evolving.²⁷

Treatment selection is anchored to severity, prior response, comorbidity, and patient preference, with a stated goal of remission rather than symptom reduction. Mild episodes respond to psychotherapy alone; moderate-to-severe episodes benefit from combination pharmacotherapy and psychotherapy; treatment-resistant cases warrant neuromodulation.^28-29

Pharmacotherapy

• First-line: SSRIs (sertraline, escitalopram, fluoxetine, paroxetine, citalopram) or SNRIs (venlafaxine, duloxetine) are recommended as initial pharmacotherapy by APA, NICE, and CANMAT, with comparable efficacy across agents in network meta-analyses.^28-30
• Other first- and second-line options include bupropion, mirtazapine, vortioxetine, vilazodone, and trazodone, with selection guided by side-effect profile and comorbidity.^28-29
• Tricyclic antidepressants (TCAs) and monoamine oxidase inhibitors (MAOIs) retain efficacy in melancholic and atypical depression respectively, but are second- or third-line because of toxicity and dietary restrictions.²⁸
• Adequate trial: 4-8 weeks at therapeutic dose before declaring non-response; partial responders should be optimized to maximum tolerated dose before switching.^28-29
• Switching strategies after non-response: within-class switch (e.g., sertraline to escitalopram) or between-class switch (e.g., SSRI to SNRI or bupropion); STAR*D found roughly equivalent remission rates across switch options at each step.³¹
• Augmentation strategies: aripiprazole, brexpiprazole, cariprazine, quetiapine XR, olanzapine-fluoxetine combination, and lithium have FDA or strong evidentiary support; thyroid hormone (T3) augmentation has long-standing but lower-quality support.^28,32
• Treatment-resistant depression (typically defined as failure of two adequate trials): intranasal esketamine plus an oral antidepressant is FDA-approved; IV racemic ketamine has substantial evidence but is off-label.^8,33
• Maintenance: continue effective treatment for at least 6-9 months after remission of a single episode; indefinite maintenance is reasonable after three episodes or two severe episodes.²⁸

Psychotherapy

• Cognitive behavioral therapy (CBT) has the largest evidence base; effect sizes versus waitlist are moderate-to-large, comparable to antidepressants in mild-to-moderate MDD.³⁴
• Interpersonal therapy (IPT) is similarly effective and particularly useful in postpartum depression and bereavement-related episodes.³⁴
• Behavioral activation matches CBT in head-to-head trials with simpler training requirements.³⁴
• Mindfulness-based cognitive therapy (MBCT) reduces relapse in patients with three or more prior episodes.³⁵
• Combined pharmacotherapy and psychotherapy outperform either alone for moderate-to-severe and chronic depression.^28-29

Neuromodulation

• Electroconvulsive therapy (ECT) remains the most effective acute treatment for severe MDD, with response rates of 60-80% and superior efficacy in psychotic, catatonic, and treatment-resistant depression.³⁶
• Repetitive transcranial magnetic stimulation (rTMS) targeting the left dorsolateral prefrontal cortex is FDA-approved for MDD after one antidepressant failure; theta-burst protocols shorten session time.³⁷
• Vagus nerve stimulation (VNS) has FDA approval for chronic or recurrent treatment-resistant depression after four failed trials, with modest acute benefit and possible long-term gains.³⁸
• Deep brain stimulation remains investigational; trials targeting the subcallosal cingulate and ventral capsule/ventral striatum have shown mixed results.¹¹

Adjunctive

• Aerobic exercise at 30-45 minutes most days reduces depressive symptoms with effect sizes comparable to psychotherapy in mild-to-moderate MDD.³⁹
• Bright light therapy is first-line for seasonal pattern depression and adjunctive in non-seasonal MDD.⁴⁰
• Sleep regularization, particularly addressing insomnia, improves depression outcomes; CBT for insomnia (CBT-I) is preferred over chronic hypnotic use.¹²
• Omega-3 fatty acids (EPA-predominant) and S-adenosylmethionine (SAMe) have limited evidence as monotherapy and modest evidence as adjuncts.²⁸
• Brexanolone (IV) and zuranolone (oral) are FDA-approved for postpartum depression; zuranolone is also approved for MDD in some labels but not currently endorsed as first-line.^9,17

Antidepressants are generally well tolerated, but no class is benign, and the harms picture extends beyond the medication itself to the chronicity of the underlying illness. Discontinuation is its own clinical event.

Common adverse effects

• SSRIs and SNRIs: nausea, headache, insomnia or somnolence, sexual dysfunction (30-70%), weight gain on chronic use.^28,42
• Bupropion: insomnia, anxiety, dry mouth, dose-dependent seizure risk.²⁸
• Mirtazapine: sedation, weight gain, increased appetite.²⁸
• TCAs: dry mouth, constipation, urinary retention, blurred vision, orthostasis, sedation, weight gain.²⁸

Serious or rare adverse effects

• Serotonin syndrome with serotonergic combinations, including SSRIs with MAOIs, linezolid, methylene blue, or tramadol; presents with mental status change, autonomic instability, neuromuscular hyperactivity.⁴³
• Hyponatremia (SIADH) on SSRIs, particularly in older adults within the first weeks.⁴²
• Increased upper GI bleeding risk with SSRIs, additive with NSAIDs and anticoagulants.⁴²
• QT prolongation with citalopram >40 mg/day (>20 mg/day in patients over 60), TCAs, and ziprasidone.²⁶
• Hepatotoxicity with duloxetine, nefazodone, agomelatine.²⁸
• ECT: cognitive effects including anterograde amnesia (typically transient) and retrograde autobiographical memory loss (more variable).³⁶

Discontinuation and withdrawal

• Antidepressant discontinuation syndrome occurs after abrupt stop or rapid taper of agents with short half-lives (paroxetine, venlafaxine); fluoxetine is least likely.⁴⁴
• Symptoms include flu-like symptoms, insomnia, nausea, imbalance, sensory disturbances ("brain zaps"), hyperarousal — distinct from relapse.⁴⁴
• Slow taper over weeks to months is recommended, particularly after long-term treatment.⁴⁴

Limitations of the evidence base

• Most antidepressant RCTs are 6-12 weeks, limiting long-term efficacy and harm data.⁴⁵
• Publication bias inflates apparent efficacy; FDA reanalyses including unpublished trials reduce effect sizes by approximately one-third.⁴⁶
• Trial populations exclude many real-world patients (suicidal, comorbid substance use, complex medical illness), limiting generalizability.⁴⁵
• Active-comparator and head-to-head trials are scarce; most evidence pits drug against placebo.⁴⁵

Age, reproductive status, and medical comorbidity reshape both the differential and the treatment plan. Generic guidelines under-serve these patients without modification.

Pediatric and adolescent depression

• Fluoxetine and escitalopram are the only SSRIs with FDA approval for adolescent MDD; sertraline is approved for pediatric OCD only.⁴⁷
• The TADS trial showed combined fluoxetine plus CBT outperformed either alone in adolescent MDD.⁴⁸
• The TORDIA trial supported switching plus CBT in SSRI-resistant adolescent depression.⁴⁹
• Increased monitoring is required in the first month given the FDA pediatric suicidality black-box.⁴¹

Geriatric depression

• Late-onset depression (after age 60) is associated with vascular changes, cognitive impairment, and higher all-cause mortality.⁵⁰
• Sertraline, escitalopram, and mirtazapine are reasonable first-line; avoid paroxetine (anticholinergic) and TCAs in frail older adults.²⁶
• Hyponatremia, falls, fractures, and drug-drug interactions are amplified concerns.²⁶
• ECT has favorable efficacy and tolerability in older adults with severe or psychotic depression.³⁶

Perinatal depression

• Untreated depression carries risks to the pregnancy including preterm birth, low birth weight, and impaired infant attachment.¹⁷
• Sertraline is the most-studied SSRI in pregnancy and lactation and is generally considered first-line; paroxetine is associated with a small absolute increase in cardiac malformation risk and is typically avoided in the first trimester.¹⁷
• Brexanolone (IV) and zuranolone (oral) are FDA-approved for postpartum depression.^9,17
• Postpartum psychosis is a psychiatric emergency requiring inpatient evaluation; risk of suicide and infanticide is elevated.¹⁷

Comorbid medical illness

• Post-stroke depression occurs in approximately one-third of survivors and responds to SSRIs; treatment may improve functional recovery.⁵¹
• Cardiovascular disease: sertraline and citalopram (≤20 mg in older adults) have the best cardiac safety data; avoid TCAs.^5,26
• Cancer: depression is underdiagnosed; SSRIs and bupropion are reasonable, with attention to fluoxetine and paroxetine inhibition of tamoxifen activation via CYP2D6.⁵
• Parkinson disease: SSRIs and SNRIs are first-line; bupropion and TCAs may have some benefit on motor symptoms but are limited by side effects.⁵¹

Comorbid substance use

• Concurrent treatment of depression and substance use produces better outcomes than sequential treatment.⁵²
• SSRIs are first-line; bupropion is favored when tobacco use disorder coexists.⁵²
• Avoid benzodiazepines for anxious depression in patients with alcohol or sedative use disorders.⁵²

Cultural considerations

• Depression presents with somatic complaints across many cultures, and idioms of distress shape symptom report.⁵³
• Stigma reduces treatment-seeking and adherence; matching language and explanatory model improves engagement.⁵³

Most patients improve with treatment, but recurrence is common and full functional recovery often lags symptomatic remission. Suicide risk is elevated across the lifetime course, not only during acute episodes.

Outcome metrics

• Acute response (≥50% symptom reduction) on first-line SSRI: 50-60%; remission: 30-40%.³¹
• Cumulative remission across four sequential STAR*D steps: approximately 67%.³¹
• Median time to response is 2-4 weeks; full benefit may require 6-12 weeks.²⁸

Recurrence and chronicity

• Recurrence within five years is approximately 50% after a single episode and rises with episode count.¹⁴
• Approximately 10-20% of MDD becomes chronic, meeting persistent depressive disorder criteria.¹⁴
• Predictors of poor course: residual symptoms, early onset, chronic stress, comorbid anxiety or substance use, family history.¹⁴

Mortality

• Standardized mortality ratio for MDD is approximately 1.7-2.0 in cohort studies, driven by suicide and cardiovascular disease.^5,54
• Lifetime risk of suicide death in MDD is 4-6% in clinical cohorts.⁴
• Approximately half of all suicide decedents had a depressive disorder.⁴

Functional outcome

• Functional recovery lags symptomatic remission by months to years.¹⁴
• Cognitive symptoms (concentration, decision-making) often persist into remission and predict workplace impairment.¹⁴

Suicide risk assessment is the single highest-stakes task in depression care, and the most common reason for emergent psychiatric presentation. Disposition is a clinical judgment, not a checklist output.

Suicide risk markers

• Static risk factors: prior attempt (the strongest single predictor), family history of suicide, male sex, older age, chronic medical illness, recent psychiatric hospitalization (highest risk in the first month post-discharge).^18,55
• Dynamic risk factors: active suicidal ideation with plan and intent, hopelessness, severe insomnia, agitation, recent loss, command auditory hallucinations, access to lethal means.^18,55
• Warning signs: giving away possessions, sudden calm after distress, finalizing affairs.¹⁸

Hospitalization criteria

• Active suicidal ideation with plan and intent, recent attempt, command hallucinations, severe self-neglect, or inability to maintain safety in the community.¹⁸
• Psychotic or catatonic depression typically warrants admission for ECT or intensive observation.^15-16
• Voluntary admission is preferred when feasible; involuntary commitment thresholds vary by jurisdiction.¹⁸

Acute management of agitation

• De-escalation, environmental modification, and oral medication (e.g., olanzapine, lorazepam) are preferred over IM agents when feasible.⁵⁶
• Reserve restraints for imminent danger; document indications and reassessment.⁵⁶

Means restriction and safety planning:

• Lethal means counseling — particularly firearm access — reduces suicide death.⁵⁵
• Stanley-Brown safety planning intervention has evidence for reducing suicidal behavior post-ED visit.⁵⁵
• 988 Suicide and Crisis Lifeline (U.S.) provides immediate telephone and text crisis support.¹⁸

Several core questions in depression care remain contested, and clinicians should hold their positions with appropriate humility. The evidence base is large but uneven, and post-marketing data continue to reshape practice.

Active debates

• Antidepressant efficacy versus placebo: meta-analyses including unpublished data suggest a smaller effect size than older estimates, with debate over clinical significance, particularly in mild depression.⁴⁶
• The serotonin hypothesis: a 2022 umbrella review challenged the simple monoamine deficiency model; clinical efficacy of serotonergic agents does not require that model to be true, but public messaging has shifted.⁷
• Pharmacogenomic testing (e.g., CYP2D6, CYP2C19 panels): industry-funded trials show modest benefit; independent reviews and current APA/NICE guidance do not endorse routine use.²⁷
• Ketamine and esketamine: rapid efficacy is established, but durability, abuse potential, and optimal dosing schedules remain unsettled.^8,33
• Psilocybin-assisted therapy: phase II trials show promise for treatment-resistant depression; FDA breakthrough designation granted, but no agent is currently approved.⁵⁸
• Antidepressant withdrawal: severity and duration are now recognized as more substantial than earlier estimates; calls for slower hyperbolic tapering are growing.⁴⁴
• Inflammation and depression: anti-inflammatory adjuncts (e.g., celecoxib, infliximab in elevated-CRP subgroups) have promising but inconsistent results.¹⁰

Guideline disagreements

• APA and CANMAT generally support combination pharmacotherapy plus psychotherapy for moderate-to-severe MDD, while NICE places more emphasis on stepped care starting with low-intensity interventions.^28-29
• Maintenance duration recommendations vary across guidelines from 6 months to indefinite, depending on episode count and severity.^28-29

• A major depressive episode requires at least five symptoms for at least two weeks, including either depressed mood or anhedonia.¹
• The DSM-5-TR removed the bereavement exclusion from MDD; a major depressive episode can be diagnosed in the context of grief.¹
• Persistent depressive disorder requires at least two years of depressed mood in adults (one year in children).¹
• Premenstrual dysphoric disorder requires prospective daily ratings across at least two cycles.¹
• Disruptive mood dysregulation disorder is diagnosed between ages 6 and 18 with onset before age 10 and cannot coexist with bipolar disorder.¹
• Lifetime prevalence of MDD in the U.S. is approximately 21%, with a female-to-male ratio of about 2:1.^1-2
• Twin heritability of MDD is approximately 30-40%, lower than bipolar disorder or schizophrenia.⁶
• Antidepressants carry an FDA black-box warning for increased suicidal ideation in patients younger than 25.⁴¹
• STAR*D demonstrated cumulative remission of approximately 67% across four sequential treatment steps.³¹
• Fluoxetine is the only SSRI with FDA approval for pediatric MDD (ages 8 and older); escitalopram is approved for adolescent MDD (ages 12 and older).⁴⁷
• ECT is the most effective acute treatment for severe MDD with response rates of 60-80% and is treatment of choice for psychotic and catatonic depression.³⁶
• Citalopram doses above 40 mg/day (above 20 mg/day in patients over 60) carry an FDA warning for QT prolongation.²⁶
• Lifetime suicide risk in MDD is approximately 4-6% in clinical samples, with prior attempt the strongest predictor of completed suicide.^4,18
• A history of mania or hypomania reclassifies the diagnosis as bipolar disorder and contraindicates antidepressant monotherapy.¹⁹
• Postpartum psychosis is a psychiatric emergency with elevated suicide and infanticide risk and typically warrants inpatient admission.¹⁷

No external funding. No conflicts of interest declared. Peer-review status: pending.